Electrode materials having high transparency (permeability) to visible light have been used as an electrode for display devices, such as plasma display panels, liquid crystal display devices, electroluminescence display devices and the like.
Conventional transparent conductive materials used for this purpose include, for example, tin oxide-base, zinc oxide-base, antimony oxide-base, and indium oxide/tin oxide-base (ITO) materials. These metallic oxides can easily form a film as a transparent conductive film on a glass or ceramic substrate. Conventional methods for the formation of such transparent conductive films include, for example, vacuum deposition, sputtering, CVD, and coating.
Among these conventional methods, vacuum deposition, sputtering, and CVD are unsatisfactory in respect of cost and mass productivity because film formation apparatuses used in these methods are complicated and expensive. The so-called "sol-gel process" has been proposed in order to solve these problems. Transparent conductive films formed by the coating method are not yet satisfactory in quality.
The so-called "photolithography" is known as a method for patterning the transparent conductive film formed on the substrate. Specifically, the conventional positive-working patterning method comprises the steps of: evenly coating a resist (a positive-working photosensitive resin) on the surface of a transparent conductive film formed on a substrate; drying the coating to form a photosensitive layer; exposing the photosensitive layer through a mask having a predetermined pattern; removing exposed areas with a developing solution; and conducting etching using the resist in unexposed areas as a mask. On the other hand, the conventional negative-working patterning method comprises the steps of: providing a negative-working photosensitive resin; conducting exposure in the same manner as described above; removing unexposed areas with a developing solution; and conducting etching using the resist in exposed areas as a mask to from a pattern.
In the above display device having a transparent conductive film, when the display of a color image is contemplated, color filters composed of color matrixes of the so-called "RGB" (red, green, and blue) should be disposed between a glass front substrate constituting a image display surface and the above transparent electrode. Further, if necessary, a light-shielding layer is formed in the boundary between each two of the RGB regions from the viewpoint of improving the contrast of the displayed image.
Light emitted from the display device through such color filters is separated into respective colors of RGB, and the separated RGB light are subjected to additive color process in a desired combination permitting color images of all color tones to be displayed.
The above methods for the formation of a patterned electrode have hitherto been carried out in the art. They, however, involve many steps suffering from problems, such as a problem of storage stability of the resist, a problem of the sensitivity of the resist, a problem of even coating of the resist, and problems of exposure and development. This unfavorably renders the production process complicated and, in addition, incurs increased cost. Printing of a coating liquid containing ingredients for forming a transparent conductive film in a pattern form followed by heating is considered as a method for solving these problems. In this method, however, it is difficult to form a fine pattern on the order of microns or submicrons, and, hence, the formed fine pattern is utterly unsatisfactory in accuracy.
Further, in the prior art, combining a transparent electrode with a color filter is indispensable for the application to a color display device, and, moreover, even a very small defect is unacceptable for the color filter, requiring a strict quality control in the production of the color filter, inevitably posing a problem of increased cost. That is, the problem involved in the color filter is added to the problems involved in the conventional transparent electrode.